Field of the Invention
The present invention relates to a three-dimensional imaging system, and more particularly, to a three-dimensional imaging system based on a stereo hologram, in which images composed of sub-images having the same vertical-horizontal resolutions which are generated at plural image projection modules having a two-dimensional arrangement structure are projected to a prism array plate or a transmission-type diffusion plate and then are converted into light points, i.e., image points by a microlens array. And a diffusion plate used as an image display screen is also mounted to a position at which an image expanded from an image point intersects with images expanded from the adjacent image points.
Description of the Related Art
Recently, three-dimensional imaging technologies, such as 3D cinemas, 3D TVs, 3D monitors or the like, for realizing 3D stereoscopic images have been developed. Representative methods of realizing 3D stereoscopic images include a system using 3D glasses and a multi-view imaging system.
A system for obtaining 3D effect using 3D glasses has inconvenience of wearing 3D glasses and a problem of image distortion. However, 3D products using 3D glasses are very well received by consumers due to high speed display, maximized depth of stereoscopic images through 3D glasses, changeability of viewing position and high resolution corresponding to the resolution of the display panel for both left and right eye images.
A multi-view imaging system has characteristics of allowing a viewer to change viewing position and minimizing image distortion which is a major problem of a 3D imaging system using 3D glasses. However, because resolution of an image projected to a viewer's eyes at a position within a viewing zone is too low due to limitation in resolution of a display panel, 3D products using a multi-view imaging system have not been well received by consumers and are still not fully commercialized.
But the resolution problem is not the major problem in the multi-view imaging system. The major problem is that it cannot generate a natural 3D image that causes no eye fatigue for viewers. In order to provide 3D images without eye fatigue, a multi-view imaging system should at least be constituted to project composite images providing a continuous parallax to a viewer's eyes at a viewing position within the viewing zone (“3-D imaging for creating real world like environments”, IEEE Proceedings, V101(1), pp 190-205, 2013).
In order to accomplish this, the number of multi-view images and resolution of each view image should be comparable to that of a flat panel display, and the arrangement distance between two adjacent view images should not be recognized at the viewing position. The resolution of image projected to a viewer's eyes at a viewing position is given by the number of multi-view images, and the resolution of each view image should be high in order to provide continuous parallax. The only way of realizing this is to convert each of the view images into a light point and to form a two-dimensional array of the light points, which has a minimum gap between the light points. The representative example capable of achieving this is a Zebra hologram (U.S. Pat. No. 7,227,674, “Active digital hologram displays”, registered on Jun. 5, 2007).
The Zebra hologram is a kind of two-dimensional stereo hologram, in which each view image is focused to a point on a photographic film and made as an image hologram with a reference beam. To make an array of point holograms, each view image within a multiview image array is displayed on a spatial light modulator (SLM), then focused to an image point on the photographic film and recorded as a point hologram, i.e., a point image hologram. Then next view image is displayed on the SLM and again recorded as a point hologram plate by shifting the photographic film for a designed distance in both horizontal and vertical directions. The arrangement order of these point image holograms is the same as each view image within the multiview image array. It may be possible theoretically for realizing an electronic version of the Zebra hologram. However, the actual possibility of realizing the Zebra hologram is extremely low because of cost and structural problems: Arranging the two-dimensional image points with the resolution of a display panel and with a gap between adjacent image points unperceived by a viewer, with use of a display device and other required components for making image point will cause the problems.
One of the methods of solving this problem is the focus light Array (“Ocular Accommodation by Super Multi-View Stereogram and 45-View Stereoscopic Display”, IDW'96, Proc. of the 11th International Display Workshops, PP489-492, 1996). Such a focus light Array, similar to a method of arranging multi-view images at pixel cells in a general contact type 3D imaging apparatus only having horizontal parallax (Jung-Young Son and Bahram Javidi, “3-Dimensional Imaging Systems Based on Multiview Images” (Invited Paper), IEEE/OSA J. of Display Technology, V1(1), pp 125-140, 2005), corrects the same position pixel from each view image in a one-dimensional multiview image array, then arrange them to the order of the image in the multiview image array as a pixel cell and focused them in to a point on the display screen in the order of the pixel in each view image by a two dimensional scanner. Since each light point is expanded, each pixel in the point will be separate angularly from its neighboring pixels. The net result of this angular separation induces the effects of the multiview images superposed by pixel by pixel order, which are propagating with different angles.
However, such a method has a problem in creating images capable of generating continuous parallax at a viewer's position because it is very difficult to make hundreds of pixels be in each pixel cell.
Recently, a method of recording a pixel cell as a beam of line light on a rewritable photographic plate has been reported (“An Updatable Holographic Display for 3D Visualization”, Journal of display technology, V4(4), pp 424-430, 2008). This method is similar to the focus light array, but only needs scanning in a horizontal direction because a unit pixel cell is focused to a beam of line light. However, because the photoplate doesn't allow recording in real time, it is difficult to display a video image. Additionally, because a hologram recording device for continuous recording and deleting should be included, this method can be hardly used for display.